andygeiss/ecs

package ecs

// Entity is simply a composition of one or more Components with an Id.
type Entity struct {
    Components []Component `json:"components"`
    Id         string      `json:"id"`
    Masked     uint64      `json:"masked"`
}

// Add a component.
func (e *Entity) Add(cn ...Component) {
    for _, c := range cn {
        if e.Masked&c.Mask() == c.Mask() {
            continue
        }
        e.Components = append(e.Components, c)
        e.Masked = maskSlice(e.Components)
    }
}

// Get a component by its bitmask.
func (e *Entity) Get(mask uint64) Component {
    for _, c := range e.Components {
        if c.Mask() == mask {
            return c
        }
    }
    return nil
}

// Mask returns a pre-calculated maskSlice to identify the Components.
func (e *Entity) Mask() uint64 {
    return e.Masked
}

// Remove a component by using its maskSlice.
func (e *Entity) Remove(mask uint64) {
    modified := false
    for i, c := range e.Components {
        if c.Mask() == mask {
            copy(e.Components[i:], e.Components[i+1:])
            e.Components[len(e.Components)-1] = nil
            e.Components = e.Components[:len(e.Components)-1]
            modified = true
            break
        }
    }
    if modified {
        e.Masked = maskSlice(e.Components)
    }
}

// NewEntity creates a new entity and pre-calculates the component maskSlice.
func NewEntity(id string, components []Component) *Entity {
    return &Entity{
        Components: components,
        Id:         id,
        Masked:     maskSlice(components),
    }
}

func maskSlice(components []Component) uint64 {
    mask := uint64(0)
    for _, c := range components {
        mask = mask | c.Mask()
    }
    return mask
}